Equatorial aminopyridine ligands stabilize an unusual straightly bridging mode in dimeric dysprosium(III) single-molecule magnets

Due to the ionic feature of the lanthanide ions, to straightly bridge two lanthanide (Ln) ions is rather challenging though this bridging mode is much beneficial to suppress the zero-field quantum tunneling of the magnetization (QTM) for single-molecule magnets (SMMs), a kind of nanosized magnetic materials for high-density information storage and magnetic resonance imaging contrast agent. Here we used an unusual terminal amino pyridine ligand which utilizes extensive supramolecular interactions to stabilize such an unusual linear bridging mode and obtained a series of such dimeric Ln(III) complexes - {[LnL_A(4-NH₂py)₅]₂(µ-Cl)}[BPh₄]₃ (For L_A^- = 1-AdO^-, 1Ln; for L_A^- = ^tBuO^-, 2Ln; Ln = Dy, Gd). More uniquely, the bridging chloride sits in the center of two improper rotation symmetry related Ln(III) ions with local C_5v symmetry. The dimeric compounds 1Dy and 2Dy exhibit much slower low-temperature magnetic relaxation and thousands of times longer relaxation times at 2 K (τ_2K = 2706.89 and 1437.05 s for 1Dy and 2Dy) compared to the diluted ones with the approaching magnetic property of the C_5v motifs (τ_2K = 0.77 and 1.29 s for 1Dy@1Y and 2Dy@2Y). Though magnetic interactions mediated via the chloride bridge in both 1Dy and 2Dy are weak and antiferromagnetic, it is still very effective due to such a linear geometry to reduce the QTM effect in SMMs.